I built mine to a very high spec but that was over 2 years ago.
Prices have fallen considerably since i built this system and you can get a more powerful desktop now for less than the £600 the CPU cost on its own.
Since you ask............
Spec is AMD64 x2 FX-60 CPU overclocked to 2.93 ghz watercooled
DFI Lanparty Skt 939 SLI Mobo
Dual NVidia 7800 GTX 256MB SLI watercooled GPU`s
2 Gig Corsair 3500 LL Pro Ram
Creative Fatal1ty Sound
Hyper 600W psu
Dell 20" WFP screen
Logitech THX 2.1 speaker system